With the rapid development of information technology, demand for improved flat panel displays is surging. To satisfy such a demand, flat panel displays such as slim, light-weight, and low power consuming flat panel displays are being developed. Particularly, LCDs with improved features such as high resolution, color illuminating accuracy, and image quality are being developed and applied to various devices such as notebook computers and desktop computers.
Generally, an LCD includes a lower array substrate having pixel electrodes on one side, an upper color filter substrate having common electrodes facing the pixel electrodes, and liquid crystal filled between the lower array substrate and the upper color filter substrate. When a voltage is applied between the pixel electrode and the common electrode, an electric field is generated in the liquid crystal to change the arrangement of the liquid crystal molecules and thereby change the light transmittance. The LCD displays images by utilizing the change in the light transmittance of the liquid crystal.
In detail, FIG. 1 shows a partial sectional view of an LCD according to the related art, in which, for clarity reasons, only one common electrode, only one pixel electrode corresponding to the common electrode, and liquid crystal filled between the common electrode and the pixel electrode are illustrated.
Referring to FIG. 1, an LCD includes a lower array substrate 10 having a pixel electrode 26, a thin film transistor (T) corresponding to the pixel electrode 26, and a transparent first substrate 5a. The thin film transistor (T) is formed on the first substrate 5a and it includes a gate electrode 12, an active layer 16, ohmic contact layers 18a and 18b, a source electrode 20a, and a drain electrode 20b. Though not shown, the gate electrode 12 and the source electrode 20a are respectively connected to a gate line and a data line that cross at right angles to each other to define a pixel region.
The pixel electrode 26 is made of transparent conductive material and it is formed at the pixel region. Also, the pixel electrode 26 is electrically connected to the drain electrode 20b of the thin film transistor (T) through a contact hole 24.
Reference numerals 14 and 22 denote an insulating layer and a passivation layer, respectively. The insulating layer 14 is formed to insulate the gate electrode 12, and the passivation layer 22 is formed to protect the thin film transistor (T).
Further, the LCD includes an upper color filter substrate 50 facing the lower array substrate 10 and a liquid crystal 30 filled between the upper color filter substrate 50 and the lower array substrate 10. The upper color filter substrate 50 includes a transparent second substrate 5b spaced apart from the first substrate 5a, an opening defined under the second substrate 5b to face the pixel electrode 26, and a black matrix 52 formed under the second substrate 5b to face the thin film transistor (T). The black matrix 52 prevents light from passing therethrough, such that light from the pixel electrode 26 can pass through the upper color filter substrate 50 while light from other portions cannot pass through the upper color filter substrate 50.
Further, the upper color filter substrate 50 includes a color filter 54, an overcoat layer 56, and a common electrode 58. The color filter 54 is formed beside the black matrix 52 at a position corresponding to the pixel electrode 26 of the lower array substrate 10 to produce color. The overcoat layer 56 is formed below the color filter 54 to protect the color filter 54 and smooth the uneven surface, and the common electrode 58 is formed on the overcoat layer 56 with a transparent conductive material.
Since the LCD itself does not have a light emitting component, a backlight unit (not shown) is provided behind the LCD as a light source. Therefore, the LCD can display various images by changing the molecular arrangement of the liquid crystal 30 when the backlight unit emits light toward the liquid crystal 30.
To display color images with the LCD, the color filter 54 is included in the LCD as a component. Referring to FIG. 2, the color filter 54 includes repeatedly arranged red, green, and blue sub-color filters 54a, 54b, and 54c, each allowing light having a corresponding wavelength to pass therethrough. By adjusting the amount of the red, green, and blue colors, an accurate color reproduction can be obtained through a combination of the three colors.
Though the structural relationship between the black matrix 52 and the color filter 54 is changed in FIG. 2 when compared with FIG. 1, this change will be understood by persons of skill in the art as an obvious change.
Pigment dispersion, dyeing, and electro-deposition are usually used to form a color filter. In a typical pigment dispersion method, a substrate is coated with resin containing a dispersed polyamide pigment and then a pattern is formed on the coated substrate using photolithography. The pigment dispersion method is widely used since it provides an increased processing margin, and higher heat-resisting and light-resisting characteristics. Particularly, the pigment dispersion method is useful for large LCDs.
However, the pigment dispersion method is disadvantageous in that the coating and photolithography operations are successively carried out to form the red, green, and blue sub-color filters, thereby complicating the manufacturing process. Also, it increases the cost due to expensive manufacturing equipment.
FIG. 3 is a schematic sectional view of a photosensitive sheet used as a dry film for a thin-film coating method according to the related art. Referring to FIG. 3, a photosensitive sheet 60 includes a cover film 62, a color photosensitive layer 64, an oxygen barrier layer 66, a cushion layer 68, a base film 69, and an anti-static layer 70 that are sequentially formed in this order. The anti-static layer 70 is provided to eliminate static electricity.
The cover film 62 and the base film 69 are provided to protect the cushion layer 68, the oxygen layer 66, and the color photosensitive layer 64 from impact, dust and the like. The cover film 62 and the base film 69 will be removed after a color filter is formed using the photosensitive sheet 60. Depending on the pigment contained in the color photosensitive layer 64, the photosensitive sheet 60 can be used for fabricating a red sub-color filter, a green sub-color filter, or a blue sub-color filter.
The color photosensitive layer 64 includes a photopolymerization type photosensitive composition, which contains an organic pigment (for a red, a green, or a blue), a binder, a photopolymerization initiator, and a functionality monomer. During a color filter fabricating process, the photosensitive layer 64 is attached to a substrate and becomes a red, a green, or a blue sub-color filter by a selectively scanned light. When a color filter is sequentially formed using red, green, and blue photoconductive sheets, the cushion layer 68 moderates the unevenness of the previously formed sub-color filter and facilitates the attachment of the next photosensitive sheet to the substrate. For this purpose, the cushion layer 68 is made of flexible, transparent material.
The oxygen barrier layer 66 preserves the photosensitivity of the color photosensitive layer 64 and prevents a light-exposed portion of the photosensitive layer 64 from dispersing.
When compared with other methods such as a pigment dispersion method, the thin film coating method of fabricating the color filter with the photosensitive sheet is advantageous to simplify the process and the manufacturing equipment. In the thin film coating method, however, chemical solutions such as a stripping solution and a developing solution are repeatedly applied to remove residual cushion and color photosensitive layers of the previously formed sub-color filter, thereby complicating the process and impacting the previously formed sub-color filter.